The immune response is dramatically attenuated during aging. There are a number of factors that contribute to this phenomenon, one of which is an intrinsic defect in CD4 T cell activation. T cell activation takes place in the context of the immunological synapse, where receptors, cytoskeletal elements, and signaling molecules are organized into discreet domains at the T cell: APC interaction site. In the mature synapse the central region, cSMAC, contains the TCR, CD28, signaling components (PKCtheta), and secretory components. The peripheral region, pSMAC, contains LFA-1 and associated proteins talin and RAPL. The phosphatase, CD45, is recruited to the site of T cell: APC interaction, but largely excluded from the synapse. Recent evidence indicates that TCR signaling takes place in microclusters that form at the outside of the synapse and the cSMAC is a site of downmodulation of TCR signaling. In contrast, we have found that CD28 costimulation occurs within the cSMAC region, through the recruitment of PKCtheta and upregulation of IL-2 transcription. In addition, we have found that LFA-1-dependent formation of the pSMAC is required for the exclusion of the CD45 and this correlates with an increase in proximal signaling through the TCR. Thus, T cell costimulation through CD28 and LFA-1 may be mediated through the organization of proteins within the immunological synapse. There is good evidence that CD28 and LFA-1 functions are diminished in T cells from aged individuals. Thus the central hypothesis of this application is that aging results in a specific defect in the ability to target CD28 and/or LFA-1, or their associated proteins, to the cSMAC or pSMAC respectively and this results in a decrease in proximal T cell signaling that will account in part for the intrinsic defect in T cell activation in CD4 T cells from aged individuals. We will test this central hypothesis in 2 Aims: (1) Determine whether CD28 signaling within and/or outside the immunological synapse is downmodulated in T cells from aged mice and (2) Determine whether LFA-1 adhesion and/or immunological synapse organization is disrupted in T cells from aged mice. We will use TCR transgenic, CD28-deficient and LFA-1-deficient mice and a combination of immunofluorescent microscopy, live cell imaging, and molecular analysis. We will determine whether aging effects T cell: APC adhesion the kinetics, efficiency, or magnitude of recruitment and organization of TCR, LFA-1, CD28, or associated proteins into the immunological synapse. We will determine whether there is a corresponding defect in LFA-1 and/or CD28-associated signaling events and whether there is an alteration in the functional consequences these costimulatory signals. Finally, if a defect is noted in any of these events we will address the specific molecular process that accounts for a loss in LFA-1 and/or CD28 function during aging. The immune response is dramatically attenuated during aging in part due to a defect in T cell signaling. The overall goal of this project is to determine the precise cellular and molecular events that account for this defect. We hope that understanding the mechanism behind this aging process will facilitate the development of specific immuno-enhancers that can counteract these events and promote effect immune responses in older individuals. [unreadable] [unreadable] [unreadable]